Groove Tubes and Valve Arts/Shuguang are the only companies with true reproduction KT66s. Groove Tubes current production KT66s are the same as the Valve Arts I believe. The GT KT66HP has been discontinued for quite some time now. The Tung Sol and JJ reissues are a different tube in a KT66 bottle. I thought the Tung Sols were cool sounding, but sound more like a 6550.